The corn kernel is composed largely of starch, fiber, fat, and protein. Most of the corn protein is contained in what is commonly referred to as the gluten fraction. Untreated corn protein has little commercial value except in animal feed. It is insoluble in water except at high pH levels (above 10.5), and is also insoluble in organic solvents, while being partially soluble in some aqueous organic solvents. These poor solubility characteristics severely limit its usefulness.
An object of this invention is to provide modified corn protein derivatives which may be cast from an aqueous solution to form a film of significant commercial value. A film cast from a highly alkaline aqueous medium (above pH of 10) is extremely friable, and thus unsuitable for the usual coating and unsupported-film uses. If an alternative solvent is used, problems involving the environment and health immediately arise.
Starting materials for the process of this invention may be commercial corn gluten, purified corn gluten, commercial zein, or purified zein.
Commercial corn gluten contains starch, fat, and fiber, in addition to protein. The most prevalent protein in corn is zein, a prolamine. The process of separating zein from the other proteins in corn is facilitated by the ability of zein to dissolve in certain solvent systems (as described below) while the fiber, starch, and the rest of the corn proteins remain as an insoluble residue.
The solvent system may comprise water and any of several alcohols, or water containing either an organic or inorganic base or a detergent. A nonpolar solvent, such as hexane, may be used to further purify the zein after solvent extraction. Such a purification step will remove fat and pigments.